Opitz [Birth Defects, 1993, 1:3-37] postulated that sporadic defects of blastogenesis generally are highly lethal and have a low recurrence risk. We have observed that mothers of infants with blastogenetic defects have more previous abortions than mothers of children with nonblastogenetic defects or than mothers of control infants. Thus the high lethality of blastogenetic abnormalities may be responsible for the spontaneous abortions, and there may be a potential for an increased recurrence risk in some cases. Our results also show that the increased rate of spontaneous abortions is not similar for all blastogenetic defects, since it is not elevated in mothers of infants with neural tube defects (NTD). Further, our analysis does not confirm the relationship between spontaneous abortions in the preceding pregnancy and the occurrence of NTD previously reported by other authors.